Glutamate-gated chloride channels, or H-receptors, have been identified in arthropod nerve and muscle (Lingle et al, 1981, Brain Res. 212: 481-488; Horseman et al., 1988, Neurosci. Lett. 85: 65-70; Wafford and Sattelle, 1989, J. Exp. Bio. 144: 449-462; Lea and Usherwood, 1973, Comp. Gen. Parmacol. 4: 333-350; and Cull-Candy, 1976, J. Physiol. 255: 449-464).
Invertebrate glutamate-gated chloride channels are important targets for the widely used avermectin class of anthelmintic and insecticidal compounds. The avermectins are a family of macrocyclic lactones originally isolated from the actinomycete Streptomyces avermitilis. The semisynthetic avermectin derivative, ivermectin (22,23-dihydro-avermectin B1a), is used throughout the world to treat parasitic helminths and insect pests of man and animals. The avermectins remain the most potent broad spectrum endectocides exhibiting low toxicity to the host. After many years of use in the field, there remains little resistance to avermectin in the insect population. The combination of good therapeutic index and low resistance strongly suggests that the glutamate-gated chloride (GluCl) channels remain good targets for insecticide development.
Glutamate-gated chloride channels have been cloned from the soil nematode Caenorhabditis elegans (Cully et al., 1994, Nature 371: 707-711; see also U.S. Pat. No. 5,527,703 and Arena et al., 1992, Molecular Brain Research. 15: 339-348) and Ctenocephalides felis (flea; see WO 99/07828).
In addition, a gene encoding a glutamate-gated chloride channel from Drosophila melanogaster was previously identified (Cully et al., 1996, J. Biol. Chem. 271: 20187-20191; see also U.S. Pat. No. 5,693,492).
Despite the identification of the aforementioned cDNA clones encoding GluCl channels, it would be advantageous to identify additional genes which encode R. sanguineus GluCl channels in order to allow for improved screening to identify novel GluCl channel modulators that may have insecticidal, acaricidal and/or nematocidal activity for animal health, especially as related to treatment of tick and mite infestation in dogs, cats, cattle, sheep and other agriculturally important animals. The present invention addresses and meets these needs by disclosing novel genes which express a R. sanguineus GluGl1 and R. sanguineus GluGl2 channel wherein expression of these R. sanguineus GluCl RNAs in Xenopus oocytes or other appropriate host cells result in an active GluCl channel. Heterologous expression of a GluCl channel of the present invention will allow the pharmacological analysis of compounds active against parasitic invertebrate species relevant to animal and human health, especially in the treatment of tick infestations in dogs and cats. Heterologous cell lines expressing an active GluCl channel can be used to establish functional or binding assays to identify novel GluCl channel modulators that may be useful in control of the aforementioned species groups.